A notebook personal computer (notebook PC) is an example of an electronic apparatus. There is a known detachable expansion apparatus for the notebook PC. Such an expansion apparatus is referred to as, for example, a port replicator, a docking station, or an expansion adaptor. A port replicator increases the number of connectors for connecting the notebook PC and external devices and allows the notebook PC to be carried while keeping cables connected to the external devices.
Notebook PCs of various different types and models are commercially available. Port replicators of various different models matching those of the notebook PCs are also commercially available. Even if a notebook PC and a port replicator allow the use of connectors conforming to the same standard, a notebook PC and a port replicator should not be used in combination if their models do not match. If an unmatching combination of notebook PC and port replicator is used, the notebook PC may not operate normally, and damage due to short-circuiting may be imposed to the internal circuits of the notebook PC.
In the related art, there is a known structure for preventing incorrect insertion and incorrect attachment that includes, for example, a plurality of protrusions attached to the edge section of a printed circuit board and a plurality of engagement holes fitted with these protrusions.
It is, however, not preferable for a notebook PC to have a special structure, such as that in the related art, for preventing incorrect insertion and incorrect attachment. Such a structure limits the design flexibility of the notebook PC.
Such a problem is common for notebook PCs and also various different apparatuses.